The aim of this research is to understand the structure and assembly of adhesion pili found on pathogenic bacteria, thereby providing insight into how the architecture of these pili supports their role as a virulence factor. Bacterial survival and colonization require attachment of the bacteria to hosts. In many stains, this process is initiated and maintained by pili; in Escherichia coli that cause pyelonephritis, adhesion and virulence depend on P-pili. Hib-pili expressed on the surface of Haemophilus influenzae mediate H. flu's colonization of the upper respiratory tract, and thus its ability to cause diseases such as childhood meningitis, otitis media, and pneumonia of the elderly. As bacteria become more resistant to traditional antibiotics, it is important to develop new therapies against bacterial infections. Structural information about adhesion pili will provide a basis for future rational design of new therapies to prevent bacterial binding or to remove pathogenic bacteria bound to the human host. The proposed research addresses this long-term goal through structural studies of bacterial adhesion pili. These studies focus on: 1) electron microscopy and three-dimensional (3-D) helical reconstruction of P-pili preserved in vitreous ice and of Hib-pili negative stain, 2) controlled damage/recovery of pili to investigate the possibility of re-formation of intact helical filaments, 3) investigation of the 3-D structure of P-pili with mutant structural proteins (pilins), to examine regions of the PapA pilin essential for their assembly into tightly coiled helical filaments, 4) bacterial attachment assays, to assess the effect of mutations and the effect of damage on bacterial binding, and 5) in vitro reconstitution of hetero-pilin polymers from chaperone-pilin complexes, to improve our understanding of the bioassembly process of a prototypical macromolecule.